Electric heater.



J. P. MONNOT.

ELECTRIC HEATER.

APPLIGATION IILED DEO.10, 1910.

1,058,380. Patented Apr. 8, 1913.

Inventor 1 Joan mormo'r, or rams, rmcn.

ELECTRIC HEATER.

Specification of Letters Yatent.

application filed December 10, 1910. Serial No. 596,708.

To all whom it may concern:

Be it known that I JOHN F. MONNOT, a citizen of the United States, and a resident of Paris, France, have invented a certain new and .useful Electric Heater,- of which the followin is a specification.

My invention re ates to electric heaters, and particularly to the heating elements thereof, and embodies an improved construction whereby the heatin coils are protected against deteriorating in uences, and wherebyineflective production of heat as radiant heat rather than'as sensible heat, is substantially obviated.

When bare resistance coils are employed 1 for heating air and the like, there is, in

effect, much loss of heat, sincemuch of the heat generated is generated as radiant heat, which. passes through'the surrounding air without raising the temperature of that air materially, and which, in effect, becomes sensible heat only when it impinges upon some solid or liquid body not transparent to heat rays. To obivate this loss, the coils must be embedded in some material, not transparent to heat, but merely conductive of heat, whereby all of the heat generated will be transmitted from the heater as sensible heat. Inthe past, this has generally been accomplished by embedding the coils in porcelain or like material; to which practice, however, there .are numerous serious disadvantages, one of whlch is that the porcelain is extremely apt to break as a result of sudden temperature changes, or unequal heating, and another of which is that the porcelain does not allow'free expansion and contraction of heating coils. A further objection is that porcelain is a rather poor conductor of heat and therefore is a poor radiating material and furthermore doesnot afford sufliciently large heating surface for contact with the surrounding air to heat the latter. v

I have found that thebest results are obtaiined by surrounding the heating coils with a finely pulverulent material of an insulating nature, inclosed within a'sealed envelop, which latter is preferably of a material having a high rate of heattransmission, such as one of the more conductive metals. The pulverulent material then performs the several functions of insulating the heating coils electrically from one another,

of excluding air from the coils and thereby preventing oxidation, of converting all radiant heat admitted from the coils into," senslble heat, of storing heat so that thri rise and fall of temperature of the resistance coils is relatively gradual, of cushioning the structure so that it is not liable to injury PatentedApr.8,1913.

even byexcessive jar or vibration, and of permitting free expansion and contraction of the coils.

I am aware that it has heretofore been proposed to surround electric heating coils with white sand (quartz sand) for the accomplishment. of some ,of the functions above mentioned; but such heaters have been in effect inoperative, at least for more than very moderate temperatures, since quartz and quartz sand and like substances, I

though good insulators at ordinary atmospheric temperatures, become quite conductive of electricity at temperatures of and above 300 centigrade; the effect of the use of quartz sand therefore is to short circuit the heating coils, reducing their resistances greatly, and therefore substantially destroy ing the heating value of the apparatus and making it extremely wasteful of current.

have discovered, however, that there are substances, capable of existing in the pulverulent form, at temperatures of and above 300 centigrade, which are still good insulators at and above such temperature. One such substance is plaster of Paris (calcium sulfate); another is slate; these materials and other materials which also have the property of remaining substantially nonconductive, at temperatures such as 300 centigrade and over, may thereforebe used successfully'to surround theheating coils of an electric resistance heater.

use as a filling, some material which is sub stantially non-conductive, not only-at a tsupport of non-conducting material-pref-- erably material of a refractory nature; I

In the 0011-. struction of my heating element therefore, I

have found ordinary earthenware suitable for the '.Upon this support is wound a resistance wire 2, of which -3 and 4 are the terminal conductors, while 5 is a conductor leading to an intermediate point of the resistance coil. These three conductors preferablypass through the center of the support 1, to and through the end cap' herein+ after mentioned, and it will be obvious that, by suitable switching means, wherebyconductors 3 and 4, or 3 and'5, or 4 and 5', or 3, 4 and5, are placed in circuit, various comgbinations,of-resistance may be obtained, and

grade and over,

l therefore various heating effects may be realized, and the degree of heat generated maybe regulated. 1 6 designates an envelop, preferably'a metallic envelop, surrounding the support 1 and between which envelop and support there is a space preferably as narrow as is consistent with the cushioning action of the filling material, filled with pulverulent insulating material 7 of the character above mentioned; that is, a material which is a non-conductor from ordinary atmospheric" temperatures to temperatures of 300 centiverulent throughout this temperature range. The interior of.- the support 1 is preferably filled with the same material.

This envelop and which remains pulis closed at the bottom by a head 8 and at the top by sealing material 9. I Customarily also I provide a further top covering 10.

-; In constructing this heating element, the, various. parts are well dried, preferably be- 1 with the resistance coil thereon has been placed withintheenvelop,

.foreassembling, and whenv t shpport 1 and the pulprisonedL-between, the: particles of the verulent matel 'ial and clinging to theysides -and-the top capis applied, It will air as possible:

The envelop is then tightly sealed, the conductors 3,4. and 5' being em bedded in the sealing material 9, which is i preferably a sealing material which is liquid or plastic at some-high temperature much above any temperature which the parts. of

the heating element wiIlreach in ractice, e noted f that owing toth. entire. interior of the envelop beingflmactically filled with the pulverulentgmateljial-g,theonly' air which the en.- velopi contains, aftersealing, is the slight amount; 1 off-{attenuated =air remaining im- 1 pulofthe parts; this amount being extremely smll: I The oxygen .of theiair so imprisoned will speedily unite with the, metal of the heating coil, if that met-albe vone which is readily;oxidized, hut-the amount of oxygen containedgwithingthe heating element, is at 'teria 1s use under ordinary conditions. I have dis covered that such fragility is not due to oxidation as has been supposed, but is due to changes resulting from too rapid heating and cooling of the metal. The pulverulent material 7 of my heatingelement, and the support 1 for the resistance coil have, collectively, a relatively large heat-storing capacity, which, enforces slow heating up and slow cooling of the resistance coil, the effect on the metal of which is equivalent to that of slow annealing; so that I have found that heating coils so protected and surrounded are not subject to the deterioration previously mentioned, but to the contrary, the-metal retains its ductility after long use. i The pulverulent material 7 is capable of yielding sufiiciently to permit substantially free expansion and contraction of the heating coils, and to cushion the parts so that mechanical injury is obviated. Such filling material also intercepts the rays of radiant energy emitted from the heating coils, converting same into sensible heat and conducting such heat to the envelop, from which it is radiated to the outer air or-other medium surrounding said heating envelop. w 5

To insure eflicient transmission of heat from the resistance conductor through the. pulverulent filling material and the metallic envelop to the outside air or other surrounding medium, it is important that the space between the resistance conductor and the metallic envelop, that is to say, the space occu material, s all be as small as is consistent with the described cushioning action of the pulverulent material. It is also extremely important that the filling material be as non-conductive of electricity as possible;

ied by the pulverulent filling hence the choice of a material which re- Y mains a substantial non-conductor at temperatures of ,or even, above 300? also the useof the sealing material 9 which "hermetically, seals the contents of v the metallic -envelop, absolutely preventin entrance'of air, and,1-in so doing, abso utely preventing the entrance of moisture which,

if it entered, would impair the insulation and lead to short-circuitmg.

For the erabl employ plaster of ,Paris, as this madoes not become temperature, an terial even at high temperature.

lastic'or molten. if at high centigrade,

pulverulent filling material I pref is very finely pulverulent;

is a good. insulating ma- It will be obvious that this heating element, may be made in various forms and sizes and of various constructions,

What I claim is 1. An electric heating element comprising an envelop having hermetically sealed within it an electric resistance conductor embedded in a pulverulent mass of material which is substantially non-conductive of electricity from ordinary atmospheric temperatures to 300 centigrade.

2. An electric heating element comprising an envelop having hermetically sealed within it an electric resistance conductor embedded in a mass of pulverulent plaster ofParis.

3. An electric heating element comprising an envelop having within it a refractory support and an electric resistance conductor mounted upon said support, the space between said support and walls of the envelop being filled with a pulverulent mass of material which is substantially non-conductive of electricity from ordinary atmospheric temperatures to 300 centigrade, said envelop provided with means hermetically sealing its contents within it.

In testimony whereof I afiix my signature, in the presence of two witnesses.

JOHN F. MONNOT.

Witnesses: H. M. MARBLE, D. A. DAVIES. 

